The normal adult human heart in women weighs <or = 350g and in men, <or 400 g. The occurrence of heart weights in humans >1000 g is exceedingly rare. During the past 30 years, approximately 10,000 human adult hearts with various types of cardiovascular diseases have been examined in this laboratory. Of that number, 30 weighed >1000 g. The most common (15 patients) cause of the massive cardiomegaly was aortic regurgitation with or without other volume lesions, such as mitral regurgitation or ventricular septal defect. Pressure lesions as the cause of massive cardiomegaly was far less common: 4 patients had aortic valve stenosis, but all also had associated aortic regurgitation or mitral regurgitation. Cardiomyopathy is a rare cause of massive cardiomegaly. Of >200 patients with idiopathic dilated cardiomyopathy studied at necropsy in this laboratory, none had hearts weighing >1000 g. Of 70 patients with cardiac amyloidosis extensive enough to cause cardiac dysfunction, none had massive cardiomegaly. During the past 30 years, we have studied at necropsy 220 patients with hypertrophic cardiomyopathy (HC) and 200 of them were >20 years of age. Of this latter number, 8 had hearts weighing >1000 g. Thus, HC needs to be added to the list of causes of massive cardiomegaly. What led to the massive cardiomegaly in our 8 patients is unclear.